The present invention relates to an electrical system, such as a vehicle electrical system, whereby two generators, whose output voltages are regulated via two corresponding voltage regulators, may sequentially deliver electrical power to one or more electrical subsystems. Each of the electrical subsystem may comprise at least one of an electrical load and a stored energy source such as a battery. In an electrical system where two or more electrical subsystems are present, the system further operates to isolate the two or more electrical subsystems while sequentially delivering electrical power to the electrical subsystems. In the latter configuration, the system may be further configured to protect against overcharging the two or more electrical subsystems. The following description in this section will focus on the third system configuration utilizing two electrical subsystems for describing the invention as it may readily be applied to the other two system configurations.
The vehicle electrical system comprises two electrical subsystems, each of which includes electrical loads and a battery. The system further comprises two generators and two associated voltage regulators which operate to provide electrical power to the two electrical subsystems sequentially at a first or common regulation voltage. A first generator is coupled with the two electrical subsystems via an isolating means whereby electrical power may flow from the generator to the two electrical subsystems but the electrical power may not flow from individual electrical subsystems to one another or the generator. This configuration is ordinarily utilized in vehicle electrical systems where one electrical subsystem comprises a starter and a first battery, dedicated for the vehicle startup, and the other electrical subsystem comprises the remaining electrical loads in the vehicle and a second battery. In applications where the two electrical subsystems require more electrical power than the first generator is capable of producing, a second generator provides electrical power, via a sequencing means, to meet the deficiency.
Isolation between the two electrical subsystems is desirable and/or required in order to insure that the vehicle's engine can be started even after one set of batteries is discharged or if there are other problems with one of the electrical subsystems. Other sophisticated electrical systems have been employed to insure that the electrical power delivery is managed as a function of the vehicle operating conditions. For instance, in a commonly assigned U.S. Pat. No. 7,202,574 entitled “System and Method for Electric Energy Switching and Control in a Vehicle,” and its progenies, hereby incorporated by reference in their entireties, a control device determines the vehicle's operating conditions and facilitates the transfer of electrical energy between systems of electrical energy sources and their associated electrical loads based on the vehicle operating conditions. The device further determines the operating conditions of the systems of electrical energy sources and their associated electrical loads and facilitates the transfer of electrical energy between them in accordance with said operating conditions.
In addition to having isolated electrical subsystem in the vehicle electrical system, sequential electrical power delivery in the system is also advantageous for the following reasons. Electrical systems, such as those implemented in modern vehicles, include complex electronics and electrical equipment. Such electrical systems are normally comprised of an internal combustion engine and a generator. The engine supplies the generator with mechanical power and the generator converts it into electrical power for the electrical system consumption.
As the number of electrical components increase, the generator's electrical output power must also increase. This is accomplished by either increasing the size of the generator or employing multiple generators in the vehicle electrical system. In a vehicle electrical system where two generators are utilized to meet the electrical power demand, sequential power delivery is desirable because concurrent power delivery can lead to oscillation between the two generators. In a vehicle electrical system where two generators are coupled with two electrical subsystems in parallel, electrical power demand causes the two generators to compete for electrical power delivery and, hence, electrical power generation oscillates between the two generators.
The two generators are, in turn, coupled with one or more prime movers, such as an internal combustion engine or a hydraulic engine. In a vehicle electrical system where the first generator is coupled with an internal combustion engine and the second with a hydraulic engine, it is desirable to provide electrical power to the electrical subsystems sequentially, first from the first generator and then from the second generator. It is well known that internal combustion engines are more efficient in power conversion than hydraulic engines and as such it would be more efficient to draw electrical power from the first generator first and engage the second generator only when the first generator is overloaded.
Aside from efficiency considerations, it may be further desirable to utilize the first generator more often than the second. This is because the coupling mechanism, typically a belt drive mechanism, between the first generator and internal combustion engine, is easier to assemble and less expensive to replace, than the components utilized in a coupling mechanism between the second generator and hydraulic engine. As such, it is desirable to configure the vehicle electrical system where electrical power delivery is sequential, i.e., first from the first generator and second from the second generator, hence most of the operating hours are accumulated by the first generator. Additionally, in applications where acoustic noise minimization is a significant part of the vehicle electrical system, it is desirable to sequentially use the generator that is coupled with the prime mover which produces the least audible noise before engaging the other generator.
Conventional voltage regulators operate to maintain the output voltage of the generator at a constant voltage. As the number and operational complexities of electronic components in the vehicle electrical system increase, the voltage regulator must accordingly provide system monitoring and protection in addition to voltage regulation. As such, control devices are utilized that couple with generators to monitor and manage electrical power distribution throughout the electrical system in addition to maintaining the output voltage of the generator at a regulation/common/system voltage.
For instance, the commonly assigned U.S. Pat. No. 7,276,804, entitled “Voltage Regulator With Improved Protection and Warning System,” and its progenies, hereby incorporated by reference in their entireties, discloses a vehicle electrical system voltage regulator with improved electrical protection and warning means that discerns and responds to regulator, generator, or vehicle electrical system operation and malfunctions. The regulator includes monitoring, control, and protection circuits with a phase signal monitor, a field switching circuit that operates the field coil in response to electrical power demands, and a field enable switch in series with the field regulating switch. The phase monitor and protection circuit ascertains and transmits generator rotational motion for use by the monitoring and control circuit in discerning the various operating conditions. The monitoring and control circuit operates on the field switching circuit to meet the electrical power demands and provide multi level fault protection to include field switching circuit reconfiguration to continue operating under various fault conditions. A warning and diagnostic system incorporating visual indicators and communication lines provide descriptive system information for use by the vehicle's operator and computer network, respectively.
In the commonly assigned U.S. Pat. No. 7,466,107, entitled “System and Method for Electric Current and Power Monitoring and Control of a Generator,” its progenies, hereby incorporated by reference in their entireties, the control device measures a voltage drop across a conductor in a generator to determine and control the total generator output current. A temperature of the conductor is also measured to improve the accuracy. The control device may further improve on the accuracy by compensating for the electrical current through a field coil that may power the generator. The control device may be used in combination with a generator in a vehicle electrical system. Other system parameters may be monitored to improve on the system monitoring, diagnostics, and control.
The present electrical system further provides for monitoring and control of the electrical system. Specifically, the voltage regulators operate to measure battery type and temperature and adjust the regulation voltage accordingly. The electrical system also may be configured so that the voltage regulators can communicate system information with one another or the vehicle computer system. Furthermore, the voltage regulators are configured to sense system voltage at various points so as to insure safe and proper operation of the vehicle electrical system and the electronic components within the electrical system. In addition to monitoring multiple system voltage sense signals, the regulators may be configured to monitor their corresponding generator's output power controller, such as monitoring the duty cycle of the generator's field coil, in order to improve the diagnostic process.
Although various systems have been proposed which touch upon some aspects of the above problems, they do not provide solutions to the existing limitations in providing electrical power sequentially from two generators, while isolating two or more associated electrical subsystems and protecting against overcharging said electrical subsystems. For example, the Wolf patent, U.S. Pat. No. 7,335,998 entitled “Device for Supplying Voltage to the Loads of an Onboard Electrical System of a Motor Vehicle, Using a Plurality of Generators” discloses a device for supplying voltage to the loads of an onboard electrical system of a motor vehicle which includes a first generator, a regulator allocated to the first generator, a second generator, a regulator allocated to the second generator, and a control apparatus. The control apparatus is connected to at least one, and possibly to both, of the regulators, and the control apparatus supplies these regulators with control signals on the basis of which the loading of the generators is compensated. However, the generators in the Wolf electrical system provide electrical power concurrently and suffer from the same shortcomings of undesirable electrical power oscillation and lower efficiency that are eliminated using sequential electrical power delivery.
In Farber et al., U.S. Pat. No. 4,757,249 entitled “Vehicle Dual Electrical System” a vehicle electrical system includes dual alternator/battery sets separately connected to separate non-critical electrical loads, and both connected through a diode circuit to a critical electrical load. A starter switch connects both batteries to the engine starter motor. Although the disclosure discusses two generators supplying electrical power to a critical load via a diode, the electrical system is not configured for sequential electrical power delivery, or more specifically, the two generators do not operate sequentially.
The Stroud patent, U.S. Pat. No. 4,347,473 entitled “Dual alternator power system for motor vehicle” discloses an emergency vehicle having dual batteries, one of which is employed for supplying power to the electrical system of the vehicle chassis and the other of which is employed for supplying power to the emergency equipment, dual alternators driven by the engine are provided for charging the batteries. The output of each alternator is connected to the input of its regulator and to both batteries whereby both alternators will be on at all times when the engine is running and will share the load on either or both batteries. However, the Stroud system provides no sequencing control over the two generators and as such it suffers from the same limitations as discussed above.
In an electrical system, such as the one disclosed here, where two or more generators are used to provide electrical power to the electrical system, it is desirable to draw electrical power from the generators sequentially. Where two or more electrical subsystems are present, it is further desirable to isolate the electrical subsystems so that one or more of the electrical subsystems may be dedicated to serve the operational conditions of the vehicle. Where sequential electrical power delivery and isolation are required in an electrical system, protection against overcharging the electrical subsystems becomes an essential aspect of the electrical system.
The present electrical system is configured to address all of the limitations of conventional electrical systems as discussed above. In addition to sequential power delivery, the electrical system may be configured to accommodate two or more electrical subsystems and provide electrical isolation between the two electrical subsystems. Where two or more electrical subsystems are present, the present electrical system may be configured to prevent overcharging the electrical subsystems by monitoring their corresponding charging voltages. Although not a limitation, it is desirable, and the present system may be configured, to utilize two identical voltage regulators so as to reduce the costs of parts, service, and maintenance of the electrical system. Monitoring of various voltages at various sense points is made in order to insure proper voltage regulation of the electrical system. The present system may be further configured to monitor the generators' output power controllers to improve the diagnostic process.